(A) Scope of the Invention
This invention relates to polyesters including copolyesters produced by condensation reactions of polymethylene glycols and dicarboxylic acids or reactive derivatives thereof, polyester multifilament partially oriented feed yarns suitable for draw falsetwist texturing, and to an improved process for producing such polyester partially oriented multifilament feed yarn.
(B) The Prior Art
The drawing (or drawing and texturing) of undrawn (including partially oriented) multifilament polyester feed yarns has long been known in the prior art. Werner Roth and Rudi Schroth (Faserforsch u. Textiltech., 1960, II, No. 8, pp 353-359) demonstrated in 1960 the natural and maximum draw ratios of polyester filaments spun at spin takeup speeds of from 400-4000 meters per minute. British 777,625 (published June 26, 1957) taught the simultaneous drawing and texturing of polyester filaments. A most recent description of a typical partially oriented polyester multifilament feed yarn in terms of break elongation (70-180%), birefringence (of at least 0.025), crystallinity (of less than 30%), relative viscosity (of at least 18), boil-off shrinkages (of 40-60%) and low interfilament boundary coefficient of friction, is contained in U.S. Pat. No. 3,772,872.
It is also well-known to chain branch polyester polymers in order to obtain better dyeability, oil-stain release or low pilling in the fiber. Such chain branched polyesters are described in U.S. Pat. Nos. 2,895,946; 2,905,657; 3,033,824; 3,669,935; 3,669,933; 3,671,494; 3,668,187, 3,668,188; 3,669,925; and 3,576,773. These special properties are incorporated into polyester fibers by or in conjunction with the use of chain branching agents in amounts of about 0.2-.45 mole percent of tetra functional chain branching agents such as pentaerythritol, and 0.5-0.7 mole percent of trifunctional chain branching agents such as trimesic acid for dyeability and oil-stain release. For the non-pilling polyethylene terephthalate fibers of U.S. Pat. No. 3,576,773, chain branching in the amount of y/n-2 to z/n-2 equivalent percent of n-valent chain units where n is 3 or 4, y is 0.2 and z is 2, is employed. If pentaerythritol, for example, were used, the amounts suggested are 0.1-1 mole percent, a range corresponding, in the case of pentaerythritol, to 708- 7080 ppm, or 10.32-103.2 microequivalents of hydroxyls based on one gram of the copolymer available for chain branching.
The separation of melt spinning and drawing phases in polyester filament production and the combination of drawing and texturing of polyester were effected commercially primarily to increase production speeds. So long as spinning and drawing were a part of the first phase of polyester processing, production speed was limited to the speed at which it was practical to take up the spundrawn filaments. When the drawing step was combined with texturing rather than spinning, melt spinning speeds (windup or takeup) could be increased to the maximum practical for takeup of the undrawn spun yarn without utilization of takeup potential by drawing. When the spinning speeds were increased to 3,000-4,000 ypm (2742-3656 mpm), the overall production increase achieved through postponing the drawing step to the second phase of processing was diminished somewhat by the fact that the draw ratio had been decreased by the higher spinning speeds. Were it possible to employ both the higher spinning speeds and increased draw ratios, (or yet higher spinning speeds with the same diminished draw ratios), production rates could be even further increased. Such an increase in production rate would involve lower capital expenditure for expensive equipment, and lower manpower requirements; and for these reasons any method by which the draw ratio can be increased in the partially oriented multifilament polyester intermediate yarn is of great value to the industry. Of nearly equal significance would be a spinning throughput increase not involving a decreased draw ratio.